3D single-crystal catalysts

Metal–organic frameworks (MOFs) stand out as candidates for gas storage among porous materials with their network of cavities and channels.

However, current techniques can only make such frameworks with a single type of pores — a structural feature that considerably reduces their gas-storing capacity.

Now, a research team from Saudi Arabia, China and the USA, has created a three-dimensional single-crystal MOF with two types of nanosized pores.1 They prepared the crystals by stimulating a reaction between zinc ions and specific organic compounds on polymer spheres in the presence of two solvents.

The pores that are larger than 50 nm are categorized as macropores; whereas those smaller than 2 nm are micropores. The macropores act like large cavities and micropores as small apertures.

“It is possible to exploit both types of pores on the crystals — micropores can selectively bind to specific chemicals and macropores can facilitate transport of various gas molecules,” says Banglin Chen from the University of Texas at San Antonio, USA, one of the corresponding authors.

Besides adsorbing nitrogen at very low relative pressures, the crystals remained stable after catalysing a specific organic reaction seven times. They also facilitated the diffusion of green-light-emitting protein molecules throughout their structures more efficiently and faster than other MOF crystals.